Radio signal receiving system



Sept' 26, 1939. w, CQNRQN A 2,173,898

RADIO SIGNAL RECEIVING SYSTEM Filed March 51, 1938 M5 062 11.64am

- Gttomeg Patented Sept. 26, 1939 RADIO SIGNAL RECEIVING SYSTEM William H. Conron and Wendell L. Carlson, Haddonfield, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application March 31, 1938, Serial No. 199,086

8Claims. The present invention relates to radio signal receiving systems, and has for its principal ob-- ject to provide an improved radio signal receiving system of the superheterodyne type adapted for remote control tuning.

It is further object of the present invention to provide a remote control tuning system adapted for the preselection of a plurality of signals in a predetermined tuning range, such as the standard broadcast band or tuning range, for example.

It is a still further object of the present invention to provide, in a superheterodyne radio signal receiving system, an improved detector-oscillator circuit and control means therefor, whereby remote preselection tuning to a plurality of difi'erent signals or broadcasting stations may be effected by'simple switching circuits conveying only direct. currents.

It is a still further object of the present invention to provide a remote preselection tuning control system for a superheterodyne receiver, which may be built at low cost and adapted for small, low-priced receivers and the like.

Preselection tuning, as used herein, should be understood to mean that the receiving system may be adjusted for response in one or more signal receiving channels or for response to one or more broadcasting stations, and thereafter may be made to respond to any one of the selected signal channels or broadcasting stations by rendering the preadjusted tuning means efiective to control the response of the receiving system.

It is, therefore, also an object of the present invention to provide, in a system of the type above referred to, means for instantaneously shifting from one signal channel or broadcasting station to another with substantially no time delay between operation of the station selector means and hearing the received signals or program. By this means, it is possible to explore, in a few seconds, the program material ofiered in a group of broadcasting or signal channels.

It is also an object of the invention to provide a radio signal receiving system having remote tuning control means, with additional means for tuning the same in the conventional manner throughout a predetermined range, such as the broadcast band, for example.

The invention will be better understood from the following description, considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, the figure is a schematic circuit diagram of a superheterodyne radio signal receiving system provided with remote tuning control means, embodying the invention.

Referring to the drawing, a plurality of converter or signal mixer tubes 5, 6, I, 8 and 9, providing combined detector-oscillators, are connected in parallel through their output or anode circuits I0 with an intermediate frequency amplifier represented by the tube I I, through an intermediate frequency coupling transformer I2, which is tuned, for example, to 460 kilocycles.

The amplifier I I is coupled to a second detector of the diode retifier type, indicated at I3, through a second tuned intermediate frequency coupling transformer I4 responsive to the same frequency. Audio frequency signals are derived from the rectifier output resistor I5 through a coupling capacitor I hand the audio frequency signals are applied to an audio frequency amplifier tube I! through a volume control potentiometer I8. The tube I! is coupled to any suitable audio frequency amplifier represented by the tube l9, which in turn is connected through an output transformer 20 with a loud speaker or other sound reproducing device 2|.

The audio frequency amplifier tube I! may be of the type known as the RCA 6L7, having a control grid 22 adjacent to the cathode 23 and connected with the volume control potentiometer I8. The tube also has a second control grid, indicated at '24, connected to ground to receive a biasing potential from the cathode resistor comprising two sections 25 and 26, the latter being connected between ground and the section 25 through a switch 21. As shown, the grid 24 receives a biasing potential from both sections 25 and 26 of the self-bias or cathode resistor, while the grid 22 receives biasing potential from only the section 25, through the potentiometer connection thereto, as indicated at 28. The operation of this tube for volume control purposes will hereinafter referred to.

In addition to the audio frequency potentials derived from the resistor l5, AVC potentials are also derived therefrom through a filter resistor '29, and applied to an AVC lead 30 for the receiving system. This is provided with a suitable filter capacitor 3|.

The detector-oscillator or mixer tubes 5-9 inclusive are provided with signal input-grids 35-39 inclusive, connected, respectively, with tuned signal input circuits 40-44 inclusive, connected in A parallel at low potential sides through a lead 45, with a signal input winding 46. The latter is coupled to a signal input circuit 41 through an input winding 48. An electrostatic grounded shield 49 is provided between the windings 46 and 48, as indicated.

It will be noted that the grids 35-99, inclusive, are connected through the inductances of the tuned circuits 49-44 and through the winding 46 to the AVG lead 30, whereby AVG potentials are applied to the control grids referred to.

Each of the converter tubes 5-9 inclusive is provided with a screen electrode 50 for the signal input or control grids, and with oscillator elements comprising an anode electrode 5! and a grid electrode 52. These electrodes are connected with tunable oscillator circuil'ls for the tubes 5 to 9 inclusive, as indicated at 54-58 inclusive, and these circuits are tuned by the amount of the intermediate frequency above the tuning of the corresponding input circuit for the particular tube.

The tubes 5-9 are provided with heater type cathodes 60-84, respectively, provided with separate cathode circuits 85-59inclusive, respectively, connected selectively to ground, indicated at '10, through the contacts ll of a lselector switch 12. The switch 12 is movable to a contact I3 for grounding a remote control lead 14 connected with a remote control switch 15 having similar remote control contacts 16 for extensible leads Tlfor the cathode leads 65-69.

It will be seen that when the switch 12 is moved over the contacts ll, the cathode of the tubes 5-9 are selectively connected to ground, and when the switch is moved to the contact 13, the switch 15 is connected to ground and may be moved to operate in the same manner over the contacts 16, to ground the cathodes of the tubes 5-9 selectively at the remote control unit at the end of the leads TI and 74. This unit is indicated by the rectangle l8 and includes a remote volume control device, such as a resistor 19 having a remote control extension lead connected with acontact 8| at the switch 21.

The latter switch has a series of contacts 82 corresponding in number and position to the contacts H, for connecting in circuit the local volume control resistor 28 with the tube E1, and the contact 8| corresponding to the contact 13 in position for connecting in circuit, in place of the resistor 26, the remote volume control resistor 19, for which the return connection to ground is completed through lead 14 to contact 13 and switch 12.

A series of indicator lamns 85 are connected on one side in parallel with a supply lead indicated at 86, and on the other side selectively through a switch 81, having contacts 88 corresponding in position and number to those on the switches 12 and 2'1, to a second supply lead indicated at 89. This represents any lsuitable arrangement for indicating the tuning adjustments effected by operation of the switch 12.

The input circuit 49 and oscillator circuit 54 of the tube 5 are arranged to be variably tuned by the usual variable capacitors 90 and 9!, gang connected for unicontrol operation as indicated by the dotted connection 92, while the remaining circuits, in connection with the tubes 8-9 inclusive, are fixed tuned for producing the desired intermediate frequency in response to preselected signals or broadcasting stations, and these circuits are tunable by means of movable cores of magnetic material such as magnetite.

In order to keep the cost of the tuning system at a minimum, the signal input and oscillator circuits were developed so that they may be tuned over a limited range by moving the magnetite cores 95 through the coils. Following experiments on such coils, it was found that sufficient range could be obtained for each unit so that the number of units that would be required to cover a certain tuning range could be reduced to a minimum. It was found, for example, that four circuits as shown were sufficient to cover the standard broadcast band from 540 kilocycles to 1600 kilocycles, with suificient overlap so that any station could be selected within that band, and two lstations relatively close together could be so selected for preselection tuning. For the broadcast band, the unit including the tuning circuits 41-44 inclusive may have the following adjustment ranges:

Kilocycles 4i M 540- 80.0 42 730-1080 143 800-1185 44 1080-1600 The tuning inductances for these circuits have been found, preferably, to comprise a single layer solenoid winding, and consist of a magnetite core sublstantially long and in diameter, movable within an average coil of approximately turns of #38 enamel wire, close wound. Differing numbers of turns are used for the differing tuning ranges.

With this arrangement, a station between 540 and 730 kcs. may be tuned in on circuit 4|; a

station between 730 'and 800- kcs. on circuit 4| or 42'; a station between 800 and 1080 kcs. on circuit 42 or 53; a station between 1080 and 1185 kcs.

on circuit 43 or 44; and a station between 1185 and 1600kcs. on circuit 44. Each circuit (radio frequency and oiscillator) will betuned' to a separate station selectively with the oscillator circuits 55-58, tuned by the amount of the intermediate frequency for 60kcs., for example, above the tuning of the respective circuits 41-44.

The circuits 40' and 54 of the tube 5 are tunable throughout the broadcast band variably, in the usual manner, by the variable capacitors 90- 9 l By tuning the capacitors 90-9l'to a fifth signal or broadcasting station, preselection tuning to five different signals may be effected by the switch '12 or the switch 15 at the remote control point. The selector switching operation consists of selectively connecting to ground the cathodes of the various converter tubes, one for each preselected signal channel.

By utilizing a tube of the type havingtwo control grids, and by controlling the gain on the second control grid with the signal applied to the first, the volume of the signal output may be controlled, and this sylstem of control is employed in connection with the tube l1 and the resistor 19 at the remote control point. Since the control grid 22 is connected back to the resistor 25, variation of the resistor 19 serves only to vary the gain control potential on the control grid 24. At the receiver, the gain may be controlled by the potentiometer l8, and therefore the resistor 26 may be fixed and may be substantially half the value of the remote volume control resistor 19.

In a practical embodiment of the receiving sylstem shown, with the selector switch in the fifth position, corresponding to the energization of the tube 5 and variable tuning, the indicator lamp in the series shown at 85 for that position may be iii) From the foregoing description, it will be seen that a preselection tuning system adapted for remote control operation may be provided by simplified circuits whereby it is adapted for low priced receivers and consists in utilizing several combined oscillator-detector tubes at the input of the receiver, with their associated circuits each tuned for response to a different signal channel. The circuits are preferably tunable by means of adjustable core inductances, and one of the circuits may be variably tunable over a preselected frequency band.

In the selection of the desired fixed or adjustable signal channels, the only control operation necessary is to switch the cathode of the tube corresponding to the desired signal channel, to ground by a simple multipoint selector means. Thus the system does not depend upon any mechanical adjustment or movement other than the switching for signal selection.

We claim as our invention:

1. In a superheterodyne receiver, the combination of a plurality of converter tubes each having a signal input grid, an output anode, a cathode and oscillator electrodes, means providing a tunable input circuit for each of said control grids, and a tunable oscillator circuit for each tube in connection with said oscillator electrodes, means for applying received signals to said tunable input circuits in parallel, means for connecting said output anodes in parallel including a tunable signal output circuit responsive to a predetermined frequency, means for selectively connecting each of said cathodes to ground in said system, means for adjustably tuning a plurality of said input and oscillator circuits to predetermined fixed frequencies and means for variably tuning one of said input circuits and one of said oscillator circuits for the same tube variably throughout a predetermined tuning range.

2. In a superheterodyne receiver, the combination of a plurality of converter tubes each having a signal input grid, an output anode, a cathode and oscillator electrodes, means providing a tunable input circuit for each of said control grids,

and a tunable oscillator circuit for each tube in connection with said oscillator electrodes, means for applying a received signal to said tunable input circuits in parallel, means for connecting said output anodes in parallel including a tunable signal output circuit responsive to a predetermined intermediate frequency, means for selectively connecting each of said cathodes to ground in said system, means for variably tuning one of said input and oscillator circuits through differing tuning ranges for receiving signals variably through a predetermined frequency band, means for adjustably tuning the remainder of said input and oscillator circuits to differing predetermined fixed frequencies for receiving signals at each of a plurality of fixed frequencies in said band.

3. In a superheterodyne receiver, the combination of a plurality of converter tubes each having a signal input grid, an output anode, a cathode and oscillator electrodes, means providing a tunable input circuit for each of said control grids, and a tunable oscillator circuit for each tube in connection with said oscillator electrodes, means for applying a received signal to said tunable input circuits in parallel, means for connecting said output anodes in parallel including a tunable signal output circuit responsive to a predetermined intermediate frequency, means for selectively connecting each of said cathodes to ground in said system, means for variably tuning one of said input and oscillator circuits through differing tuning ranges for receiving signals variably through a predetermined frequency band, and means for adjustably tuning the remainder of said input and oscillator circuits to differing predetermined fixed frequencies for receiving signals selectively at each of a plurality of fixed frequencies in said band, said last named means in each circuit comprising a single layer tuning inductance, and a magnetite core therefor adjustable to vary the value of said inductance in circuit.

4. In a tuning control system for a superheterodyne receiver, the combination of a plurality of signal mixer tubes each having a tunable signal input circuit and a tunable oscillator circuit, means for applying signals to said input circuits in parallel, means providing a common intermediate frequency output circuit for said tubes, means for tuning each of said input circuits to difiering signal frequencies within a predetermined signal wave band and for tuning said oscillator circuits to frequencies differing there from by a predetermined intermediate frequency, means providing an individual grounded cathode circuit for each of said tubes and means for individually completing each of said cathode circuits to ground thereby to cause said receiver to respond to signals at said differing signal frequencies, said last-named means comprising a selector switch having contacts for connecting each of said cathode circuits to ground, a remote control unit having selector switch contacts connected with each of said cathode circuits, and means providing a contact in said first-named selector switch providing a ground connection through said second-named selector switch for said cathode circuits, thereby to provide remote control tuning of said receiver through said remote control unit.

5. In a superheterodyne receiver the combination of a plurality of signal mixer tubes each having a tunable signal input circuit and a tunable oscillator circuit, a commonintermediate frequency output circuit for said tubes, a cathode circuit for each of said tubes, selector switch means for completing said cathode circuits individually to ground, means for applying signals to said input circuits in parallel, means for applying automatic volume control potentials through said signal input circuits in parallel, means for tuning each of said input circuits to differing preselected signal frequencies and said oscillator circuits to frequencies differing therefrom for each tube by a predetermined intermediate frequency, whereby said receiver is tunable instantly to any one of said preselected signal frequencies by selectively completing said cathode circuits individually, a remote control unit including a second selector switch means, means for extending said cathode circuits to said selector switch means in said remote control unit, and means for completing a ground connection for said cathode circuits from said second selector switch means through said first-named selector switch means.

6. In a superheterodyne receiver, the combination of a plurality of signal mixer tubes, each having a signal input circuit and an oscillator circuit connected therewith and having a common intermediate frequency output circuit, means for tuning said input and oscillator circuits to differing fixed signal frequencies including adjustable core tuning inductances in a plurality of said circuits and variable tuning means in one of said signal input circuits and one of said oscillator circuits for the same tube, a cathode circuit for each tube, and means for selectively connecting said cathode circuits to ground thereby to energize said tubes selectively and to eflect tuning of said receiver selectively to said differing signal frequencies and a plurality of signal frequencies over a variable range provided by said variable tuning means.

'7. A preselection tuning control system for a superheterodyne receiver comprising, in combination, a plurality of detector-oscillator tubes, a tunable signal input circuit and a tunable oscillator circuit connected with each of said tubes, means including a movable core inductance in each of said circuits for tuning each of said tubes to produce a predetermined intermediate frequency in response to received signals at differing fixed frequencies throughout a predetermined wave band, means for tuning one of said signal input circuits and the oscillator circuit for one of said tubes variably through said Wave band, means including a coupling circuit common to said signal input circuits for applying received signals to said input circuits in parallel, means providing a common intermediate frequency output circuit for said tubes, a cathode circuit for each of said tubes, and means for selectively connecting each of said cathode circuits to ground as the sole selector means for controlling the response of said receiver to a plurality of preselected signal waves.

8. In a superheterodyne receiver, the combination of a plurality of signal mixer tubes each having detector electrodes, oscillator electrodes and a common cathode, means for applying signals to said detector electrodes in parallel and including an input circuit for each tube adjustably tunable through difierent portions of the same predetermined Wave band, an oscillator circuit connected with the oscillator electrodes of each tube, said oscillator circuits being tunable each to a frequency differing from the tuning of the input circuit for said tube by substantially the amount of a common intermediate frequency, means providing a common intermediate frequency output coupling circuit for said tubes, an intermediate frequency amplifier coupled thereto, selector switch means for individually grounding said cathodes, thereby to tune said receiver to any one of a plurality of differing signals by selectively closing the cathode circuits as the sole signal selecting means for said receiver, and means for variably tuning the signal input and oscillator circuits for one of said tubes variably through said Wave band, thereby to provide additional means for tuning said receiver throughout said wave band.

WILLIAM H. CONRON. WENDELL L. CARLSON. 

